Method for generating a dither image

Abstract

A method of, and apparatus for, dithering an image to be printed. Color component values of odd and even pixels of an image are stored in a dither cell. The dither cell is mapped to a staggered dither cell such that lines of odd pixel component values are staggered relative to lines of even pixel component values. Addressing of the staggered dither cell is determined by an address generator that also addresses a buffer storing an up-interpolated image. Corresponding values in the staggered dither cell and the buffer are compared to determine which nozzles of a printhead are fired.

1. A method of converting an image into a dithered, bi-level image for printing, comprising the steps of:
 storing an up-interpolated version of said image in a first buffer; 
 storing color component values corresponding to even pixels in first entry locations in a dither cell; 
 storing color component values corresponding to odd pixels in second entry locations in said dither cell; 
 staggering lines of said color component values corresponding to odd pixels relative to lines of even pixel values so as to form a staggered dither cell; 
 comparing each pixel value in said first buffer with its corresponding value in said staggered dither cell; and 
 outputting an instruction to print to a second buffer if said value from said first buffer is greater than or equal to said staggered dither cell value. 
 
     
     
       2. The method of  claim 1  wherein said storing of said up-interpolated image and
 said storing of said color component values are controlled by means of an address generator. 
 
     
     
       3. The method of  claim 1  wherein said storing step further includes storing said color component values in said first and second entry locations in a correct order for printing by a printhead. 
     
     
       4. The method of  claim 1  wherein said storing step further includes storing a number of color component values in one entry location, said number being determined by loading criteria of a printhead. 
     
     
       5. The method of  claim 1  wherein said storing steps further comprise storing twelve color component values in each of said first and second entry locations. 
     
     
       6. The method of  claim 5  wherein said twelve color components consist of three colors to be printed for four segments of a printhead.